Sintering and characterization of PLZT (9/65/35)

PLZT(9/65/35) obtained by association between the Pechini method (ZT) and partial oxalate (PLZT) was prepared. The stoichiometric phase and monophasic (cubic) PLZT obtained by calcination did not occur after sintering. The sintering process, by using two stages, caused a liquid phase formation due to a PbO excess (5 and 10 wt%). Samples with high density (similar to 8 g/cm(3)) and optical transparency(similar to 12%) were obtained. However, an equilibrium between the excess of PbO of sample/atmosphere PbO leads to a segregated PbO phase on the boundaries of the microstructure. A diffusion of Zr, Ti and La ions from PLZT to PbO phase promoted a stoichiometric deviation of the matrix and modified the optical and dielectric characteristics. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Synthesis and characterization of 9.5/65/35 PLZT prepared from the polymeric precursors

The 9.5/65/35 PLZT was prepared from the polymeric precursors (the Pechini and partial oxalate process) and by sintering in two stages in an oxygen atmosphere. After thermal treatment at 400 degreesC, the powders were calcinated and sintered at 1200 degreesC with slow heating and cooling rates. The second stage of sintering consisted of hot pressing at the same temperature in oxygen atmosphere. After calcination of PLZT powders obtained by both methods, as well as after sintering of PLZT obtained by Pechini process, the paraelectric cubic phase was formed. After sintering of PLZT obtained by partial oxalate procedure, small tetragonality of crystal structure was observed. After hot pressing PLZT was pseudocubic. SEM microstructural analyses were carried out of the sintering and hot pressed samples and indicated the small grain size less than 2 mum. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Hot-pressed 9.5/65/35 PLZT prepared by the polymeric precursor method

A 9.5/65/35 PLZT ceramic with a Pb-0.905 La-0.095 (Zr-0.65 Ti-0.35)(0.976) O-3 + 35 w% PbO formula was prepared using the Pechini method for powder preparation and two-step sintering in an oxygen atmosphere. Thr first step consisted of sintering at 1200 degrees C for 4 h with slow heating and cooling rates. The second step consisted of hot pressing at 1200 degrees C for 3 h, with slow heating and cooling rates and pressing pressures of 20 MPa (initial pressure) and 40 MPa (at sintering temperature). Investigations were made of the powder phase formation and powder morphology, i.e. The structure of sintered and hot-pressed PLZT ceramics. SEM microstructural analyses were carried out on the sintering and hot-pressing processes. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Preparation of 9/65/35 PLZT thin films deposited by a dip-coating process

Crack-free polycrystalline PLZT (Pb,a)(Zr,Ti)O-3 thin films with the perovskite structure were prepared by dir-coating using the Pechinis process. Lead acetate, hydrated lanthanum carbonate, zirconium n-propoxide and titanium isopropoxide were used as raw materials. The viscosity of the solution was adjusted in the range of 20 to 56 cP and the films were deposited by a dip-coating process on silicon (100) as substrate. Solutions with ionic concentration of 0.1 and 0.2 M were used. Thin film deposition was accomplished by dipping the substrates in the solution with control of withdrawal speed from 5 to 20 mm/min. The thin films were thermally treated in two steps: at 300 degreesC amid 650 degreesC. The influence of withdrawal speed. viscosity, heating rate and ionic concentration on the morphology of PLZT thin film was discussed. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Effect of Hydrogen Peroxide at 35% on the Morphology of Enamel and Interference in the De-remineralization Process: An In Situ Study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Preparation of 9.5/65/35 PLZT powders by organic precursor method

In this study the preparation of 9.5/65/35 PLZT ceramic powders were investigated. The powders with the formula Pb0.905La0.095(Zr0.65 Ti0.35)0.976O3 + 3.5 w% PbO were prepared using Pechini process and partial oxalate method. The powder phase formation, powder morphology, and green density of PLZT were shown.

Evidence for 2.35 to 2.30 Ga juvenile crustal growth in the northwest Borborema Province, NE Brazil

The c. 600 Ma Brasiliano Borborema Province of NE Brazil comprises a complex collage of Precambrian crustal blocks cut by a series of continental-scale shear zones. The predominant basement rocks in the province are 2.1-2.0 Ga Transamazonian gneisses of both juvenile and reworked nature. U-Pb zircon and Sm-Nd whole-rock studies of tonalite-trondhjemite-granodiorite basement gneisses in the NW Ceará or Médio Coreaú domain in the northwestern part of the Borborema Province indicate that this represents a continental fragment formed by 2.35-2.30 Ga juvenile crust. This block has no apparent genetic affinity with any other basement gneisses in the Borborema Province, and it does not represent the tectonized margin of the c. 2.1-2.0 Ga São Luis Craton to the NW. The petrological and geochemical characteristics, as well as the Nd-isotopic signatures of these gneisses, are consistent with their genesis in an island arc setting. This finding documents a period of crustal growth during a period of the Earth's history which is known for its tectonic quiescence and paucity of crust formation. © Geological Society of London 2009.

Indirect cytotoxicity of a 35% hydrogen peroxide bleaching gel on cultured odontoblast-like cells

The aim of this study was to evaluate the trans-enamel and trans-dentinal effects of a 35% hydrogen peroxide (H2O2) bleaching gel on odontoblast-like cells. Enamel/dentin discs obtained from bovine incisors were mounted in artificial pulp chambers (APCs). Three groups were formed: G1- 35% H2O2; G2- 35% H2O2 + halogen light application; G3- control. The treatments were repeated 5 times and the APCs were incubated for 12 h. Then, the extract was collected and applied for 24 h on the cells. Cell metabolism, total protein dosage and cell morphology were evaluated. Cell metabolism decreased by 62.09% and 61.83% in G1 and G2, respectively. The depression of cell metabolism was statistically significant when G1 and G2 were compared to G3. Total protein dosage decreased by 93.13% and 91.80% in G1 and G2, respectively. The cells in G1 and G2 exhibited significant morphological alterations after contact with the extracts. Regardless of halogen light application, the extracts caused significantly more intense cytopathic effects compared to the control group. After 5 consecutive applications of a 35% H2O2 bleaching agent, either catalyzed or not by halogen light, products of gel degradation were capable to diffuse through enamel and dentin causing toxic effects to the cells.

Exigência de treonina digestível para codornas de corte no período de 15 a 35 dias de idade

The digestible threonine (DThr) requirements for meat quails (Coturnix coturnix sp) during growing phase from 15 to 35 days of age were estimated, using 1,020 quails with 15 days of age, of both sexes, distributed in a completely randomized design, with six levels of digestible threonine-0.93; 1.00; 1.07; 1.14; 1.21 and 1.28% in diet, five replications and 34 quails per experimental unit. There was no effect on performance variables, carcass yield and chemical composition and nitrogen balance with the studied increase in digestible threonine levels. There was a linear increase in threonine intake and feed cost per kilogram of body weight gain with increasing levels of digestible threonine. It was concluded that the best level of threonine evaluated was sufficient to meet the requirements of meat quails, in the period from 15 to 35.

Acta resumida de la 72a sesión celebrada en Panamá el viernes 15 de mayo de 1959 a las 10.35 horas

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Acta resumida de la 75a sesión celebrada en Panamá el sábado 16 de mayo de 1959 a las 15.35 horas

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